Flotation of apatite



United States Patent ABSTRACT OF THE DISCLOSURE Apatite is floated from apatite-bearing rock by pulping the ground rock in ordinary hard water at ordinary room temperature using a reagent combination consisting of a fatty acid reagent, an alkyl aryl sulphonate reagent and a sulphated fatty acid reagent, conditioning the pulp with this reagent combination, aerating it, removing the apatite as a floating constituent and removing the non-float. as tailing.

The present invention relates to an improved method of mineral flotation, especially of apatite and media therefor.

Froth flotation is a widely known process and is employed in many parts of the world to concentrate desired minerals from their ores and the like. Especially in the past 30 years, with the exhaustion of the richer orebodies of many kinds, froth flotation has developed into a process of inestimable value in the separation of valuable mineral particles from the ores and the like in which they are contained.

The process comprises the flotation of particulate mineral raw material, e.g. ground, crushed or otherwise milled or comminuted mined ore for the purpose of physically liberating the desired mineral from other minerals, i.e. to obtain it as separate particles. However, the ore or the like is at this stage still a mixture of the desired and the less valuable kinds of minerals.

The milled ore or the like, with water and relatively small amounts of purposely added chemical agents, is stirred or agitated in special flotation cells to form a suspension, while air bubbles are caused to pass through the suspension. Through this action, the chemical agents will form a froth on the surface of the suspension. In the froth, a concentration of one or more species of mineral is effected, provided that all the conditions and especially the nature and quantity of the added chemical agents are suitable for the given ore.

The chemical agents used can be grouped in three classes, namely:

(i) Collectors These chemical agents have molecules which consist of a hydrocarbon section which, like oil, it not wetted by water; and a polar section which, according to theory, is attached to certain minerals under favorable conditions. In this Way, a monomolecular mantle or layer is formed, which gives the mineral concerned a hydrocarbon-like surface which does not become wet in water.

When a mineral particle which is covered in this manner makes contact with an air bubble in the pulp, it adheres to the air bubble simply because the air displaces the water on the unwettable surface of the mineral particle.

Air bubbles carry their load of mineral particles to the surface of the pulp in the flotation cell, where a froth is formed which can be removed to obtain the so-called concentrate.

7 3,405,802 Patented get. 15, 1958 It is also possible in certain cases to obtain the unwanted mineral particles in the froth, in which case the concentrate isrepresented by the non-float.

Numerous collectors are known in flotation practice or have been proposed in the technical and patent literature. Examples of these are oleic acid, linoleic acid, palmitic acidand their soaps, sodium dodecyl sulphate, sodium stearyl sulphate, sodium dodecyl benzene sulphonate, sodium butyl naphthalene sulphonate, potassium ethyl xanthate, potassium amyl xanthate, dodecyl amine hydrochloride and trimethyl cetylammonium bromide.

(ii) Modulating chemical agents This group includes a large variety of organic as well as inorganic substances. For example, sodium hydroxide or sulphuric acid are used to regulate the pH of the pulp. Other inorganic chemical modulating agents like lime have the eflect of making pyrite unfloatable during "the flotation of certain copper minerals.

Organic modulating agents include starch, gums, tannins and similar substances which, for instance, may render serpentine and related minerals less floatable in cases where magnesite or other minerals are floated.

(iii) Frothers As explained in the foregoing, air bubbles rise with adhering mineral to the surface of the pulp. If a frother is present, froth will form on top of the pulp. The desired, or in certain cases the undersired mineral is present in the froth in higher concentration than in the pulp. The froth flows over the side of the cell or is skimmed off by paddles. The froth consists of air, water, collected mineral and a quantity of uncollected mineral Which did not have suificient time to drain out of the froth, or was otherwise entrained.

Collectors like fatty acid, soap, alkyl aryl sulphonates sometimes also behave as frothers, but the best frothers are those which have a minimum of collecting properties. They are polar-non-polar molecules of the type C H O'H, amylalcohol or C I-I OH, the active constituent of the well known frother pine oil. The aliphatic alcohols used as frothers preferably have chain lengths of 5 to 8 carbon atoms, provided there is sufficient branching in the chain, alcohols in the 10 to 12 C-atom range are good frothers, but they sometimes tend to be high priced.

Although the process can often be adjusted to high efficiency for a given ore by preliminary test work, it is generally known that, for the same mineral coming from another area or sometimes also from elsewhere in the same ore-body, a set of conditions which has been found effective in one case, appears to be ineflicient in another case.

In the flotation as hitherto practised, for example, of phosphate minerals in the better known phosphate fields, use is made of sodium hydroxide and/or other alkalis, e.g. sodium carbonate and sodium silicate, or potassium or lithium alkaline compounds, together with the collector agents like fatty acid and mineral oils.

In accordance with the present invention it has been found that alkalis or alkaline agents are not necessary and in fact are undesirable in certain cases of fatty acid flotation, where it has been considered essential up to the present, or that the proportion of alkali or alkaline agents can be greatly reduced. An example thereof is the large phosphate deposit in the apatite-pyroxenite rock at Phala borwa, Transvaal, Republic of South Africa, a rock which occurs over about five square miles and to a considerable depth.

The apatite-pyroxene rock at Phalaborwa contains up to about 8% P 0 or about 20% by weight, of the phosphate mineral apatite. The apatite occurs as scattered grains in the pyroxenite body, together with the pyroxene mineral diopside, and minor quatities of micaceous minerals like vermiculite and phlogopite.

Anderson, In]. Chem, Met, Min. Soc. S.A., April 1936, pp. 287-295, describes briefly the practice using alkalis on the Phalaborwa pyroxenite ores. Since that date it was found that heating the pulp water, and using softened Water are advantageous when alkalis are used with fatty acids.

According to the conceptions existing in the prior art, the successful flotation of apatite from the pyroxenite when alkalis are used, depends on the use of softened water, and/ or the heating of the water to at least 35-40 C. to maintain a pulp temperatre in this region. While the amounts of fatty acids and alkalis for a given sample can be tested and regulated for optimum results of flotation, it is still found that a pyroxenite sample taken from another part in the same ore-body, cannot be successfully floated with the same quantities of mentioned chemical agent additions. Additional experimentation is then required to obtain flavourable conditions for the particular ore.

Under the circumstances described in the foregoing paragraph, troublesome operating conditions could arise in a production plant which concentrates phosphate by means of flotation, especially from pyroxenite. In accordance with the invention, pyroxenite ores of different occurrences, for example of apatite, can be treated by a standard method with good results, as shown in the following description.

In accordance with a specific modification of this invention, it has been found that, apart from using little or no alkalis, the use of softened water as well as increased temperature is unnecessary if the conditions of the specification are carried out.

In accordance with a preferred embodiment of the invention, the ordinary fatty acid type collector, plus organic chemical agents of the type alkyl-aryl sulphonate or alkyl-aryl sulphonic acid are used, the latter in an amount which varies between 40% and 300% of the fatty acid amount, according to the purity of the sulphonate and fatty acid used.

The alkyl-aryl sulphonic acid is obtained as a by-product of the refining of petroleum. At one step the petroleum stock is treated with oleum, which is superconcentrated sulphuric acid, and then the products of the purification reaction are separated from the lubricating oil. One of these leads to so-called green acids from which the alkylaryl sulphonates are made by direct neutralisation. There are various suppliers in South Africa, notably Shell Chemical Company, Socony-Vacuum, and South African Cyanamid Company.

In some experiments also it was found advantageous to use in addition to the fatty acid and the sulphonic acid or sulphonate, a quantity of sulphated tall oil. The quantity of sulphated tall oil used ranged from 30% to 100% of the fatty acid, which was added as a refined tall oil. The sulphated tall oil is made by the wood industry in the course of purifying the tall oil obtained.

When operating under the conditions and using the chemical agents referred to in the two preceding paragraphs in the flotation of minerals like apatite from pyroxenite, a minimum of operating control is necessary in a flotation production plant. This results in a clean concentrate, with a great reduction of the usual considerable loss of phosphate minerals like apatite in the tailings.

The expression ordinary room temperatures has the meaning attaching thereto in normal usage. Preferred temperatures in this range in accordance with the invention are 2030 C. Ordinary hard water also has its usual meaning herein and preferably indicates 50-250 parts per million of total hardness, expressed as CaCO Operation in accordance with the present invention will, moreover, result in the saving of costs on chemical agents usually used in this type of flotation.

The apatite-pyroxene rock from recovered is preferably ground.

According to one aspect of the invention the aforesaid improvements in the flotation of apatite from apatitepyroxene rock are attained by pulping the said rock in ordinary hard water at ordinary room temperature and admixing a reagent combination consisting of a fatty acid, and an alkyl-aryl sulphonate, conditioning the pulp with this sole reagent combination, aerating it, removing the apatite as a floating constituent, and removing the nonfloat as tailing. 1

In the aforesaid reagent combination distilled tall oil may be employed as the fatty acid. I

Again advantages may be obtained by admixing with the rock pulp a reagent combination consisting of distilled tall oil, sodium naphtha sulphonate and sulphated tall oil, conditioning the pulp with this sole reagent combination, aerating it, removing the apatite as a floating constituent, and removing the non-float as tailing.

A more specific embodiment of this process comprises grinding the apatite-pyroxene rock, pulped in ordinarily hard water, at ordinary room temperature, with sodium naptha sulphonate, further conditioning the mill-discharge pulp in a conditioner with tall oil and with sulphated tall oil, floating the conditioned pulp to recover the apatiteenriched froth from the apatite-depleted tailing, dewatering the froth and drying it for further use.

According to a more general aspect of the invention the flotation of apatite-bearing rocks comprises grinding the ore, then floating it using a wholly-organic reagent combination containing a fatty acid and a petroleum sulphonate made from green acid, and recovering the apatitebearing float.

In another embodiment of the process in accordance with the present invention, the flotation of apatite from pyroxenite, consists in the addition to the pyroxenite pulped in water, of an organic reagent combination consisting of fatty acid and naphtha sulphonic acid, conditioning the pulp with this reagent combination, aerating, removing the apatite as a floating constituent and discarding the non-float as tailing.

The advantages of the process in accordance with the present invention will become apparent from the following further examples as compared with the prior art, but it should 'be understood that the invention is not limited to the examples, in accordance with the invention, which have here been furnished.

Example 1 Examples from results obtained, in accordance with the invention, in the laboratory with the flotation of apatite from different types of pyroxenite ore are set out in Table 1. From these results, the advantages which this invention yields compared with the general known method in which alkalis are used as modulating agents are evident. In connection with the results given it must be taken into account that under the present conditions 36.4% P 0 is the minimum grade at which Phalaborwa phosphate concentrate is accepted by the trade.

In the comparative Experiments Nos. 78, and 96, using the same reagent combination, it is pointed out that these experiments are in accordance with the prior art, and it is clearly demonstrated that the process is liable to give poor phosphate recovery with comparatively small variations in water hardness. Proceeding to Experiment 59, which is also in accordance with the'prior art, it is shown that good results may be obtained provided the pulp is heated and softened water is used. However, pro ceeding further and practicing the prior art on the ore sample used in Experiment 65 results in a poor recovery notwithstanding the application of conditions yielding good results in Experiment 59. It is precisely such conditions which make plant operation most diflicult, and

which apatite is to be susceptible to the variations which continually occur in run of mine ore.

On the contrary the advantage attained in Experiments 21 and 65 (b), both of which follow the conditions of the invention, is the comparatively slight effect resulting from a change in the ore, whilst reagent additions require no change, and these experiments are carried out at ambient temperature without any heating, and (as compared to Experiment 59) without the expense of a water softening operation.

In all the foregoing experiments in accordance with the invention, the advantages of not adding alkaline agents are also clearly demonstrated.

Concentrate Chemical agents, lb./ton ore Percent Percent P205 recovered 0.57 fatty acid, 0.62 lb. alkyl-aryl sulphonate,

pulp temperature C 36. 7 86. 3

TABLE I.THE FLOTATION OF APAIITE FROM DIFFERENT PYROXENIIE ORES, WITH AND WITHOUT ALKALIS, IN THE LABORATORY Chemical agents, lbJton ore Concentrate Flota- Tails,

tion Type of Pulp Water Caustic Sodium Soda- Fatty Alkyl- Percent Percent Expt. pyroxenite ore temp. soda silicate ash acid aryl Percent P20 P20 N NaOH NazSiOa NaCoa Unitol sul- P 0 distridistri- DSR phonate bution bution 78 Pilot plant Tap water. 2. 0 0. 5 0 0. 3 0 39. 0 56. 2 43. 8

sample. Total hardness 116 p.p.m. 8.5% P205, 35 Tap water. 2. 0 0.5 0 0. 3 0 36. 5 88. 4 11.6

pilot plant Total hardsample. ness 95 p.p.m. 96 Ore 1: Hard 35 Tap water. 2.0 0.5 0 0.3 0 36.4 58.0 42. 0

pryoxenite Total hardore, percent ness ppm.

5 o 21 o 22 Tap water. 0 0 0 0. 5 0. 5 36. 4 88.8 11. 2

Total hardness ppm. 59 do 35 Soitened wateL... 0 0. 5 2.0 0. 3 0 36. 4 91. 0 9. 0 65 Ore 2: Vermic- 35 .d0 0 0.5 2.0 0.3 0 36.4 62.2 37.8

ulite rich pyroxenite, geireent P205= 65(1)) do 22 Tap water. 0 0 0 0.5 0. 5 36.4 81. 0 19.0

Total hardness 165 ppm.

Note Unitol DSR is a commercial refined tall oil. Its composition is as follows: Fatty acids (oleic, linoleic, palmitic), 90.1%, rosin acids 7.3%, unsaponifi ables 2.6%.

Example 2 40 Example 3 on a further ore sample The following example compares results obtained in accordance with the prior art and the present invention:

1. Prior art.Pyroxenite ore of grade 8.6% P 0 is treated by a continuous flotation process in a pilot plant with unsoftened water at 35 C., with the addition of 4 chemical agents as mentioned, and the results as obtained appear in the following table. The fatty acid used was in Comparative experiments were made between a fatty acid and alkali sulphonate on the one hand, and fatty acid and sulphonic acid derived from alkali sulphonate by acidification and extraction, on the other hand. The results are tabulated below and refer to a composite sample of borehole cores from the pyroxenite. Grinding and conditioning times are constant for the three exboth cases a mixture of near equal proportions of oleic periments:

TABLE II Reagents Results Test To mil To conditioner Percent Percent recovery P205 Reagent LbJT Reagent Lb./T grade 1 Shell naphtha sul- 0. 6 Unito1 DSR refined 0. 6 68. 2 36. 6

phonate. tall oil. Sulphonic acid 0. 6 -do 0. 6 78. 7 25. 9 d0 1.2 do. 0.6 84.4 34.3

acid and linoleic acid, plus a minor proportion of impuritiesin fact such a mixture as would be represented by a number of commercial brands of highly-refined tall oil.

Concentrate Chemical agents, lb./ton ore Percent Percent P105 recovered (a) 0.30 lb. fatty acid, 0.81 11). sodium silicate,

1.3 lb. caustic soda, pulp temperature 35 0.. 34. 2 75 (b) 0.40 lb. fatty acid, 0.9 lb. sodium silicate,

1.3 lb. caustic soda, pulp temperature 35 C-.- 36. G 62. 3

It is stressed, that under the prior art conditions, as shown in Experiment 1a of the foregoing table concentrates are often produced containing less than 36.4%, which is the minimum grade accepted by the trade. Adjusting the conditions to improve the grade in accordance with the prior art Experiment 1b results in a 12.7% loss in recovery, whereas Experiment II in accordance with It will be seen that the substitution of sulphonic acid for the alkali sulphonate (from which it was perpared) did not damage the results. In fact a substantial improvement in recovery is obtained at a small drop in grade (Experiment 3). The complete absence of added akalis shows one extreme of the invention.

Example 4 5 Development of the basic method of excluding alkalis has thusied to an improvement in average recovery (at 36.4% P grade of concentrate) on 14 diiferent samples from 72.2% to 85.1%.

The data reported in Table V were obtained by using Shell Naphtha Sulphonate (SNS) as the mill reagent. Thereafter, the second reagent, a mixture of Unitol DSR Refined Tall Oil, and Unitol S.T.O. Sulphated Tall Oil were added as the cell reagents in the conditioner. It

will be'noted that the-use of the three components in the two reagents resulted in an average recovery at 36.4% of 85.1, as compared with the much lower average recovery of.72.2% at 36.4%, when using only a two component mixture (Table III).

TABLE III.RESULTS ON 14 DIFFERENT PYROXENITE SAMPLES, USING ONLY SULPHONATE AND TALL OIL Conditioning, cell reagents, lb./ton

Pyroxenite ore sample, Recovery type Time, Unitol AP 801 at 36.4

min. DSR sulphonate Under calerete, 5 from top 2. 5 0. 6 0. 6 40. 0 5 below ealcrete, east 2. 5 0. 6 0.6 80. 0 Lumps of vermiculite..- 2. 5 0. 6 0. 6 S4. 2 Berohold comp. more than 5% P205 2. 5 0. 6 O. 6 65. 6 Borehole comp. *5%

P205 2. 5 0. 6 0. 6 72. 2 Sta ckpile, mat. under- 2. 5 06 0. 6 66. 5 2. 5 0. 6 0. 6 71. 0 2. 5 0. s 0. 6 7o. 0 2. 5 0. 6 0. 6 85. 1 2. 5 0. 6 0. 6 72. 0 2. 5 0. 6 0. 6 79. 5 2. 5 O. 6 0. 6 80. O

TABLE IV.USING UNITOL S.T.O., SULPHAIED TALL OIL IN ADDITION TO SULPHONATE AND TALL OIL IN THE FLOTATION OF 14 DIFFERENT SAMPLES OF PYROXENITE Mill reagents, lb. [ton Pyroxenite ore sample, Recovery type Shell Unitol Unitol at 36.4%

"SNS DSR S.T.O.

Under calcrete, 5' Irom top 0. 5 0. 25 0. 30 73. 0 5' below calcrete, east... 0. 5 0. 25 0. 30 83.0 Lumbs of vermiculite 0.5 0. 25 0. 30 83. 5 Borehole comp. more than 5% P2O5.-- O. 5 0. 25 0. 30 84. 2 Borehole Comp. 5%

P 0. 5 0. 0.30 84. 5 stockpile, mat. underlying calcrete O. 5 0. 25 0. 80 71. 0 As per XIII 0. 5 0. 25 0. 73. 1 Comp. of calcrete and vermiculite 0. 5 0. 25 0. 30 82. 5 0. 5 0. 25 0. 30 84. 5 0. 5 0. 25 0. 30 83. 0 0. 5 0. 25 0. 30 83. 6 0. 5 0. 25 0. 30 86. 0 O. 5 0. 25 0. 30 87. 8 0. 5 0. 25 0. 30 85. 3

TABLE V.USING SULPHATED TALL OIL IN ADDITION TO SULPHONATE AND TALL OIL ON 14 DIFFERENT PYROXENITE SAMPLES, AND SPLITTING POINT OF ADDITION BY USING SULPHONATE IN THE MILL AND THE OTHER REAGENTS IN THE CONDITIONER Mill r reagent, Cell reagents, lbs/ton Re- Pyroxenite ore 'lbsJton' covery sample, type Shell at.

S. Time Unitol Unitol 36.4%

min. DSR S.T.O. x

Under calcrete, 5

from top 0. 5 2. 5 0. 25 0. 3 76. 0 5 below calcrete, east 0.5 2.5 0.25 0.3 87.6 Lumps of vermiculite 0. 5 2. 5 0.25 0. 3 '80. 0 Comp. borehole,

more than 5% z 5 0.5 2.5 0.25 V 0.3 84.8 B orehole comp.

15% P205 0. 5 2.5 0. 2 5 0.3 85. 9 stockpile, mat. underlying calcrete 0. 5 2. 5 0. 25 0. 3 79. 5 As per XIII 0.5 2. 5 0. 25 0. 3 80. 5 Comp.,of calcrete and vermiculite"--- 0. 5 2. 5 0. 25 0. 3 81. 5

What we claim is:

1. A process for the flotation of apatite from apatitepyroxene ore which comprises:

first pulping and mixing the ore in ordinary hard water at ambient temperature with a first reagent selected from the group of substances consisting of alkylaryl sulphonic acids, naphtha sulphonic acids, petroleum sulphonic acids, and salts thereof, said reagent being employed in amounts between 40% and 300%, by weight, of the hereinafter-mentioned second reagent, I

thereafter, conditioning the pulp with the addition of a second reagent comprising a combination of fatty acid and sulphated fatty acid material the latter material being employed in an' amount of between 30% and by weight, of the fatty acid, and aerating the thus-treated ore under flotation conditions, and removing the apatite as a floating constituent. i

2. A process according to claim 1, in which the first reagent is a petroleum sulphonate.

3. A process according to claim 1, in which the second reagent comprises tall oil and sulphated tall oil.

4. A process according to claim 1 in which the ore is first ground with ordinary hard water at ambient temperature with sodium naphtha sulphonate, whereafter the resulting mill discharged pulp is further conditioned in a Conditioner With tall oil and with sulphated tall oil prior to flotation.

References Cited UNITED STATES PATENTS HARRY B. THORNTON, Primary Examiner R. HALPER, Assistant Examiner. V I 

